It is often desirable to determine the direction of a radiation source, e.g., gamma radiation, fast neutrons, etc. such as in tomography, astronomy, and civil defense applications. However, because most forms of radiation interact with matter through the processes of the photoelectric effect and Compton scattering, the angular distribution of the photoelectrons and Compton electrons (the energy forms which may be detected from radiation) are altered and skewed by these scattering events. Thus, it has been difficult to accurately determine the angle of incidence of the radiation.
Various techniques have been used to provide detectors with a directional capability. One commonly used directional detector is a collimated instrument where shielding is used to restrict the angular acceptance of radiation by the detector and to reduce background contributions from other directions. Thus, a maximum output is obtained only when an aperture in the shielding is aligned with a radiation source. In some instances, a rotating collimator aperture or multiple apertures are used to obtain source direction information. However, these collimated instruments have several disadvantages such as distortion of incoming radiation by interactions with the collimator walls, a small solid angle of acceptance when a high directional resolution is necessary thus reducing radiation intensity, and poor angular resolution when a large solid angle of acceptance is necessary.
Other directional detector designs have used filament-type detectors to obtain directional information. For example, Chupp et al., "A Direction Neutron Detector for Space Research Use," IEEE Transactions on Nuclear Science NS-13, pp. 468-477 (Feb. 1966), teaches aligning filament axes toward the radiation source to provide a directional output. As another example, Stetson et at., "A Directional Scintillation Counter for Neutrons," 6 Nuclear Instruments and Methods, pp. 94-95 (1960), suggests the use of an array of filament arrays that use the forward-peaked angular distribution of protons from n-p collisions to obtain directional effects.
In many applications, weight and portability are important considerations in selecting a detector. For example, space applications require light weight devices, and simplicity is desired since repair is not feasible. These same considerations are also applicable to mobile detectors, particularly hand held devices or devices that might require access to restricted locations.
U.S. Pat. No. 5,345,084, issued Sep. 6, 1994, to Byrd et at, and entitled, "Directional fast-neutron detector," teaches another type of directional radiation detector, which is limited to detecting fast neutrons, wherein a plurality of omnidirectional fast neutron radiation detectors are arranged in a close packed relationship to form a segmented symmetric detector. A processor arithmetically combines the incident radiation counts from the plurality of detectors to output a signal functionally related to a direction of a source for said radiation. In one embodiment of the Byrd device, four detectors are arranged in paired relationship with front-back and left-right symmetry. Output radiation counts are combined by subtracting counts from the detectors having front-back symmetry and subtracting counts from the detectors having left right symmetry. The resulting differences form a vector quantity indicating the direction for the source of the radiation. However, as stated this detector is limited to detecting the direction of fast neutrons and has a low directional resolution.
Therefore, there exists a need for a directional detector/imager of radiation sources which has a high angle of acceptance with high resolution and which can detect a plurality of different types/intensities of radiation sources. The present invention addresses this need.